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Visible Light Communication
COS 463: Wireless NetworksLecture 23
Kyle Jamieson
What is VLC• Visible light communication (VLC)
– visible light source as a signal transmitter– air as a transmission medium– appropriate photodiode as a signal receiving component
2
What is VLC• Key idea behind VLC– Eye cannot detect fast light switching but
semiconductor- based photodetector can do
3
What is VLC – Light source
4
5%
25%
60%
Light emitting diode (LED) – since 1990s§ Compact and 50% light§ Uses 2-17 watts of electricity § More than 100,000 hours lifespan
Fluorescent lamp§ White light§ 25% light§ Lifetime ~10,000s hours
Incandescent bulb§ First industrial light source§ 5% light, 95% heat§ Few thousand hours of life
Efficiency Powerusage
10%
20%
> 40%
80%
Lumens/W: 10-18
Lumens/W: 35-100
Lumens/W: 35-150
What is VLC� Light detector• PIN photodiode
• low cost, large area• limited sensitivity
• Image sensors• Charge-Coupled Device (CCD): low
cost, slow due to serial read-out
5
Motivation of VLC• Privacy-preserving
• Resilient to Interference
• Radio spectrum crunch– Ever-growing user demands meet limited radio
spectrum
6
Looking into VLC spectrum• VLC has a large frequency band
– 390 nm – 700 nm in wavelengths – 430 – 770 THz in frequency
7
Key difference from RF• RF communication works in a Non-line-of-sight
environment• VLC requires Line-of-sight between the transmitter and
the receiver
8
VLCRF signals
VLCModulation Schemes• Many conventional schemes can be applied:
– On-off keying (OOK)
– Frequency-shift keying (FSK)
– Pulse amplitude modulation (PAM)
– Pulse width modulation (PWM)
9
Current VLC Systems
10
Range (m) Data rate Modulation YearLanger et.al. 1.5 230Mb/s OOK 2010Khalid et.al. 0.5 1Gb/s OFDM 2012Kottke et.al. 0.3 1.25Gb/s OFDM 2012Sewaiwar et.al. 0.85 3Gb/s OFDM+RGB 2015